The golden era of planet finding kicked into high gear with the launch of the Kepler Space Telescope in 2009. This spacecraft nestled into an Earth-trailing orbit, then fixed its eye on a small patch of sky -- and kept it there for four years. Within that patch were more than 150,000 stars, a kind of cross-section of an arm of our own Milky Way galaxy, as if Kepler were shining a searchlight into deep space. Kepler was looking for planetary transits -- the infinitesimally tiny dip in starlight that occurs when a planet crosses the face of the star it is orbiting.

The method only works for distant solar systems whose planets' orbits, from our perspective, are seen edge-on. This way, an exoplanet is silhouetted as it passes between Kepler and its host star, reducing the starlight measured by Kepler.

"We launched Kepler, to some extent, like Magellan or Columbus went to sea, not knowing quite what we were going to encounter," said James Fanson, deputy manager in the Instruments Division at NASA's Jet Propulsion Laboratory in Pasadena, California. Fanson was Kepler's project manager when the spacecraft was launched. "We knew we were going to make history," he said. "We just didn't know what history we were going to make."

Kepler's transit watch paid off, identifying more than 4,000 candidate planets hundreds to thousands of light-years distant. So far, some 2,000 of those have been confirmed -- some of them Earth-sized planets that orbit within their star's so-called habitable zone, where liquid water can exist on a planet. Scientists are mining Kepler data, regularly turning up new planetary candidates and confirming earlier finds.

Within the Kepler Space Telesope's field of vision between two constellations—Cygnus the swan, and Lyra, the harp, is a strange star, KIC 8462852 star just above the Milky Way, noteable for the odd swarm of objects orbiting it. KIC 8462852 was emitting a stranger light pattern than any of the other stars in Kepler’s search for habitable planets. “We’d never seen anything like this star,” Tabetha Boyajian, a postdoc in the astronomy department who oversees Planet Hunter at Yale told The Atlantic. “It was really weird. We thought it might be bad data or movement on the spacecraft, but everything checked out.”

Boyajian is the lead author of a paper that explores a number of scenarios that might explain the pattern—instrument defects; the shrapnel from an asteroid belt pileup; an impact of planetary scale, like the one that created our moon. In 2011, several citizen scientists working with Boyajian flagged KIC 8462852 as “interesting” and “bizarre.” The star was emitting a light pattern that looked stranger than any of the others Kepler was watching.

Jason Wright, an astronomer from Penn State University, is preparing to publish a report on the “bizarre” star system suggesting the objects could be a “swarm of megastructures”, according to a new report. "I was fascinated by how crazy it looked,” Wright told The Atlantic. “Aliens should always be the very last hypothesis you consider, but this looked like something you would expect an alien civilization to build.”

Boyajian is now working with Wright and Andrew Siemion, the Director of the SETI Research Center at the University of California, Berkeley, writing a proposal to point a massive radio dish at the unusual star, to see if it emits radio waves at frequencies associated with technological activity.

If they observe a sizable amount of radio waves, they’ll follow up with the Very Large Array (VLA) in New Mexico, which may be able to say whether the radio waves were emitted by a technological source, like those that waft out into the universe from Earth’s network of radio stations.

Fifty years ago the physicists Freeman Dyson speculated that vast structures could ring or completely enclose their parent star. These Dyson Spheres, the work of a Kardashev Type II civilization — would be capable of drawing on the entire energy output of its star. Geoff Marcy, Professor of Astronomy at the University of California, Berkeley, who is famous for discovering more extrasolar planets than anyone else, 70 out of the first 100 to be discovered, received from the UK’s Templeton Foundation to search for Dyson spheres.

Marcy studies thousands of Kepler systems for telltale evidence of such structures by examining changes in light levels around the parent star as well as possible laser traffic among extraterrestrial civilizations. "Fermi Bubbles," which might appear as a void in visible light in spiral galaxies, is the term used by Richard Carrigan, a scientist emeritus at Fermilab, in his work on the search for cosmic-scale artifacts like Dyson spheres or Kardashev civilizations using Infrared Astronomical Satellite (IRAS) data . A Fermi bubble would grow as the civilization creating it colonized space, according to Carrigan.

As Carl Sagan observed, the time to colonize an individual system is small compared to the travel time between stars. A civilization, believes Carrigan, could engulf its galaxy on a time scale comparable to the rotation period of the galaxy, or every 225–250 million years, and perhaps shorter.

Searching for signatures of cosmic-scale archaeological artifacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization.

This type of search is called interstellar archaeology or sometimes cosmic archaeology. The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. The constraints of the anthropic principle, for example, would have to be loosened if a different type of intelligence was discovered elsewhere.

A variety of interstellar archaeology signatures could include non-natural planetary atmospheric constituents, stellar doping with isotopes of nuclear wastes, Dyson spheres, as well as signatures of stellar and galactic-scale engineering.

The concept of a Fermi bubble due to interstellar migration grew out of the the discussion of galactic signatures. These potential interstellar archaeological signatures are classified using the Kardashev scale, developed by Nikolai Kardashev, who divided civilizations into those harvesting all the energy of a planet, of a star, and of a galaxy. With few exceptions interstellar archaeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are currently under way.

According to the Kardashev scale, radio SETI might be a type 0 civilization. A type I civilization would utilize the energy available from a planet. Signals from exosolar planetary atmospheres fall roughly in this category. A Dyson Sphere, a star cloaked in broken up planetary material, would be an example of type II. Another example would be some sort of engineering of the stellar burning process suggested by Martin Beech. A civilization using all of the energy of a galaxy would be type III.

James Annis,a member of Experimental Astrophysics Group at Fermilab, has suggested that elliptical galaxies, which exhibit little structure, might be a more likely place to look for Fermi bubbles than spiral galaxies. Annis examined existing distributions for spiral and elliptic galaxies and looked for sources below the normal trend lines where more than 75% of the visible light would have been absorbed. But no candidates were found in his sample of 137 galaxies. From this Annis inferred a very low probability of a Type III civilization appearing that would be found using this search methodology.

In 1960 Dyson suggested that an advanced civilization inhabiting a solar system might break up the planets into very small planetoids or pebbles to form a loose shell that would collect all the light coming from the star. The shell of planetoids would vastly increase the available "habitable" area and absorb all of the visible light. The stellar energy would be reradiated at a much lower temperature.

If the visible light was totally absorbed by the planetoids a pure Dyson Sphere signature would be an infrared object with luminosity equivalent to the hidden star and a blackbody distribution with a temperature corresponding to the radius of the planetoid swarm. For the case of the Sun with the planetoids at the radius of the Earth the temperature would be approximately 300 ºK.

Many of the earlier searches for Dyson Spheres have looked for so-called partial Dyson Spheres where the loose shell only partially obscures the star. The Dyson Sphere investigation at Fermilab looks for so-called pure Dyson Spheres as well as partial Dyson Spheres.

Studying the M51 Whirlpool galaxy (image above), Carrigan says a rough qualitative estimate shows there are no unexplained ‘Fermi bubbles’ at the level of 5 percent of the M51 galactic area. The quest is tricky because spiral galaxy structure includes natural voids — even if a void in visible light with infrared enhancement were traced, it would be hard to regard it as anything other than natural.

The distribution of galaxies on a plot of galactic optical brightness or luminosity versus the maximum rotation velocity or radius of the galaxy follows a fairly consistent pattern. Cases lying below the typical galactic trend line reflect visible light that has been absorbed and emitted somewhere else in the electromagnetic spectrum.

Looking elsewhere, ynthetic or unnatural constituents in an exoplanet atmosphere could show a sign of ETI. The fingerprints of life, or biosignatures, are hard to find with conventional methods, but advances for eample by the ESO's VLT team in Chile team have pioneered a new approach that is more sensitive. Rather than just looking at how bright the reflected light is in different colours, they also look at the polarisation of the light, an approach called spectropolarimetry.

"The light from a distant exoplanet is overwhelmed by the glare of the host star, so it's very difficult to analyse — a bit like trying to study a grain of dust beside a powerful light bulb," says Stefano Bagnulo of Armagh Observatory, Northern Ireland. "But the light reflected by a planet is polarised, while the light from the host star is not. So polarimetric techniques help us to pick out the faint reflected light of an exoplanet from the dazzling starlight."

In the attempt to identify Dyson spheres, their use would greatly expand the useful area for activities for any culture that could build them, absorbing most or all visible light and re-radiating the energy of the star at lower temperatures. Various searches for infrared excesses around visible stars –hoping to target a partial Dyson sphere, perhaps a ring — have been attempted, but with no luck from the searches of several thousand stars. Even a pure Dyson sphere, completely surrounding its star, is not definitive because there are natural objects that mimic it, especially since dust clouds surround stars as they are born and as they die.

Carrigan used data from the IRAS spacecraft’s database of low resolution spectra, discarding objects that had been previously well categorized and narrowing the sample to sixteen sources that he calls ‘mildly interesting.’ Only three had relatively low spectral statistical fluctuations. All of the sixteen sources have some feature which clouds their identification as a Dyson sphere.

The search suggests that there are few if any even mildly interesting candidates within several hundred light years of Earth.

Carrigan observes that "a Dyson sphere does not require intent to communicate on the part of a civilization. The current detection reach is comparable to a SETI search. However there is a problem of confounding signatures from mimics such as carbon stars. Searches for potential Dyson spheres would be sharpened by developing more realistic pictures of construction scenarios including such factors as time to build and approaches to stability… "Finally it would be interesting to consider how stellar evolution might stimulate the necessity of such large scale structures with a view to looking at candidate objects in the later stage of evolution along the main sequence."

When we search for the type of structures or effects, the "signatures," interstellar archaeology, we acknowledge that they demand technologies so far beyond our own that their construction seems all but miraculous.

"We can look for Dyson spheres," Carrigan says, for example, "but scarcely imagine how a culture could build at this scale. But these are limitations of our own state of development, and they don’t keep us from extrapolating to what civilizations far older than our own might be capable of developing."

In the current search for advanced extraterrestrial life SETI experts say the odds favor detecting alien AI rather than biological life because the time between aliens developing radio technology and artificial intelligence would be brief.

“If we build a machine with the intellectual capability of one human, then within 5 years, its successor is more intelligent than all humanity combined,” says Seth Shostak, SETI chief astronomer. “Once any society invents the technology that could put them in touch with the cosmos, they are at most only a few hundred years away from changing their own paradigm of sentience to artificial intelligence,” he says.

ET machines would be infinitely more intelligent and durable than the biological intelligence that created them. Intelligent machines would be immortal, and would not need to exist in the carbon-friendly “Goldilocks Zones” current SETI searches focus on. An AI could self-direct its own evolution, each "upgrade" would be created with the sum total of its predecessor’s knowledge preloaded.

"I think we could spend at least a few percent of our time... looking in the directions that are maybe not the most attractive in terms of biological intelligence but maybe where sentient machines are hanging out." Shostak thinks SETI ought to consider expanding its search to the energy- and matter-rich neighborhoods of hot stars, black holes and neutron stars.

The Daily galaxy via The Atlantic and centauri-dreams.org, stacks.iop.org, eprintweb.org, and kurzweilai.net

Comments

If KIC 8462852 has artificial macro-structures, this will negate my personal theory that an advanced exo-civilization will technically evolve toward a nano-vrtual-world rather than construct grossly 'expensive'' (labor plus resources) macro-energy collectors like a Dyson Sphere.

I see Dyson 'Constructs' as obsolete mechanical things and, in view of far less resource-demanding nano-scale, massive-memory-quantum-virtuality, almost comic-book imaginings. This is not at all to demean Dr Dyson, but technology has moved a far, far distance beyond what was present when he drafted his thoughts. And the investment to effect such a macro-engineering project (a solar system-sized Lego device) would effectively drain too much of a civilization's resources (mineral content of habited planets, asteroids and comets, etc). Personally, I feel the answer for an advanced civ seeking massive increments in utilizable energy is to 'go nano' - to inner-migrate whole populations into virtual existence by storing personalities in massive nano-scale, memory arrays complemented with quantum computing. However, my thinking doesn't mean I will just not consider that Dyson 'Constructs will ever exist - as noted in the article just released today (http://arxiv.org/abs/1510.04606):

" The Ĝ Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. The Signatures and Information Content of Transiting Megastructures"
"... Since well motivated physical models have so far provided natural explanations for these signals, the ETI hypothesis is not warranted for these objects, but they still serve as useful examples of how nonstandard transit signatures might be identified and interpreted in a SETI context. Boyajian et al. 2015 recently announced KIC 8462852, an object with a bizarre light curve consistent with a "swarm" of megastructures. We suggest this is an outstanding SETI target."

So we can have fun surmising and proposing extra-terrestrial engineering as a possible explanation for Kepler 8462852.

It is important to consider possible explanations and mechanisms for the "unusual" luminance behavior of this star - whether or not the behavior turns out to be driven by alien technology. I offer some thoughts to seed the thinking
by more members.

OVERALL ISSUE:
IF THE ANOMALOUS BEHAVIOR OF KEPLER-8462852 IS CONFIRMED TO BE DRIVEN BY ALLIEN TECHNOLOGY?

A. How Many Advanced Alien Civilizations Might There Be?

Calculating the ratio of spatial sector (spherical) volumes (earth-to-8462852 'radius' vs Milky Way volume), and assuming Kepler-8462852 is the only appropriately advanced alien civ in our mutually shared volume sector, there might be 6,000 civs in the Milky Way galaxy with at least the technology to construct similar Dyson Systems. But, in the Hubble Universe, there would be, by a similar spatial volume ratio, 10exp20 or so advanced Dyson civs! Someone check the math. Let's hope 8462852 'pans' out. (Whether or not the Dyson construct still operates is not so important as its confirmation - although, if computer controlled and solar-energized and with Ai, the System could continue to operate for centuries after its creators have died away or left it and the star system behind!)

B. If Kepler-8462852 Luminar Variations Result from Aperiodic Attenuation of Stellar Radiance By A Non-Enveloping (Partial Blockage) Dyson Construct?

First, there would not be a message content to decode. Mostly, this would mean randomness, but it might also create a repeating 'nonsense' radiance pattern of short duration equal to the orbital period of the Dyson Construct. Second, the radiance that leaked around the Dyson Construct would give an estimate of size and distance from the star via interference patterns seen with a sufficiently resolving earth telescope.

Consider this - if Kepler-8462852 is influenced by a Dyson construct that is a computer-controlled, modulated system, the time-between-modulation peaks (via 'slow', electro-mechanical platelet re-orientation, or even the more likely case of faster, solid-state reflectance control !!) will be governed by the time to achieve acceptable SN. Such re-orientation time for a star-volume Dyson-Swarm might be fairly large, perhaps years, in our time. This would mean that overall, the observed luminar peak patterns should be examined for completeness on a long scale, regardless of the comparatively long message time (complete messages might take years, or even decades long to 'transmit'). A more sophisticated decoding approach might also assign code significance to statistically significant (1,2,etc sigma) attenuations which would greatly increase messaging 'richness'.

But,note: the attenuated signal luminance 'base shape' would differ from the naked stellar luminance by a reflectivity factor that will depend on the material composition of the Dyson-mirrors. Or, obversely, we might be able to deduce some of the ''secrets' of the alien technology used to design/create or even process some of the Dyson-construct's components. To do the latter would require perhaps substantially more telescope signal-detection-and-resolving power than available for the initial reception - perhaps more Arecibo time or use of Atacama. (There is a hint of a plan to use Green Bank).

Correction to calculations re expected numbers of 8462852-like civilizations (Kardashev Type2) in Milky Way and in the Hubble Universe:

A. How Many Advanced Alien Civilizations Might There Be?
"..... 600 civs in the Milky Way galaxy with at least the technology to construct similar Dyson Systems (Kardashev Type 2). But, in the Hubble Universe, there would be, by a similar spatial volume ratio, 10exp14 or so similarly advanced Dyson civs! (Someone check the math.) That's a lot of advanced civs but the Universe is big so we won't run into Kardashev-2's too often!..."